JPH07307140A - Mass spectrometer and ion source - Google Patents

Abstract

PURPOSE:To provide an ion beam of a good quality, excellent in convergence, where limitation of a divergence angle and that of a beam width of the ion beam are satisfied simultaneously in a mass spectrometer. CONSTITUTION:A voltage 12d of a repeller electrode 1f of an electron impact ionizing ion source 1 is input into an ion source state monitor unit 11, which outputs a prediction value 12e of a voltage applied to an extraction electrode 1g to an extraction power source 9. In the extraction electrode system, a slit of an acceleration electrode 1b is made wider than a slit of the extraction electrode 1g, and is set to approximately the same distance as that from the acceleration electrode 1b toward an ion generation region. Consequently, an electric field leaked into an ionizing chamber 1a through the slit of the acceleration electrode 1b is enlarged toward the vicinity of the ion generating region, thus efficiently extracting an ion beam 2 so as to penetrate through the slits of the acceleration electrode 1b and the extraction electrode 1g. A quantity of a current flowing through the slits is measured by an ion current monitor 8a. A voltage 12f of a convergence electrode 1d is regulated in such a manner as to maximize the current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass spectrometer, and more particularly to an ion source and a mass spectrometer equipped with a beam extraction electrode system suitable for extracting an ion beam having a small angular dispersion and a high transmittance. .

[0002]

2. Description of the Related Art FIG. 7 shows a sectional view of an ion source and a beam extraction electrode system of a conventional mass spectrometer. In the case of an electron impact ionization ion source, the ions generated by being irradiated with electrons in the ionization chamber 1a repel the repeller electrode 1f to which a positive potential is applied by a few volts from the ionization chamber 1a, and the extraction slit of the acceleration electrode 1b. Extruded from 15. Since the pushed-out ion beam 2 spreads after crossing at the crossover point 2c, the focusing electrode 1c is provided to focus the ion beam 2, and the acceleration electrode 1b and the ground electrode 1d are also provided.
In the meantime, it is finally accelerated to about 6 kV. At that time, in order to efficiently guide the ion beam 2 to the analysis unit, that is, the sector magnetic field and the sector electric field, the width and divergence angle of the ion beam 2 are controlled by adjusting the voltage of the focusing electrode 1c. Specifically, when starting up the mass spectrometer, the Faraday cup,
An ion current monitor 8a using a multiplier or a channel plate is inserted in a region where the ion beam 2 passes, and the amount of ion current passing through the exit slit 1e is measured by the ion current monitor 8a. The voltage 12f applied to the focusing electrode 1c was adjusted so that

Incidentally, there is JP-A-57-27553 as one related to the prior art.

[0004]

In the above-mentioned prior art, generally, the gap between the acceleration electrode 1b and the focusing electrode 1c is the slit 1
The width is about 10 times wider than the width of 5, and the change of the divergence angle of the beam 2 with respect to the change of the electrode voltage, that is, the position change of the crossover point 2c is extremely small. However, the optical system of the mass spectrometer is required to have a divergence angle and a beam width within a certain value at the same time. Therefore, in the conventional electrode structure in which only one electrode voltage 12f can be adjusted, the divergence angle and the beam width are restricted. It is difficult to adjust such that

An object of the present invention is to provide a highly sensitive mass spectrometer equipped with an extraction electrode system which can be easily adjusted so as to simultaneously satisfy the divergence angle and beam width constraints, and an ion source therefor.

[0006]

The above object is to provide an ion source in which ions generated in an ion generation region are extracted from a slit of an accelerating electrode into an ion beam, and the ion beam is converged by a converging electrode and emitted from an emission slit. This is achieved by providing an extraction electrode for separating the crossover point of the ion beam extracted from the slit of the acceleration electrode from the acceleration electrode by a required distance in the vicinity of the downstream of the acceleration electrode.

Further, the above-mentioned object is to provide an extraction electrode having a slit having a width smaller than that of the acceleration electrode at a position which is separated from the acceleration electrode downstream by the same extent as the distance between the acceleration electrode and the ion generation region. Can be achieved.

The above object can be achieved by setting the voltage condition applied to the extraction electrode based on the state of the ion source.

[0009]

In the conventional structure, the ion beam extracted from the accelerating electrode crosses over immediately after being extracted, so that the divergence angle becomes large. However, in the present invention, the extraction electrode is provided so that the crossover point is increased. Since the position of can be separated from the accelerating electrode, the divergence angle can be suppressed, and a high-quality ion beam excellent in focusing can be obtained. Moreover, since the voltage applied to the extraction electrode can be adjusted, the divergence angle and the beam width can be satisfied at the same time.

The principle of the present invention will be described below with reference to the drawings. FIG. 3 (a) is an electrode configuration diagram of the electron impact ionization ion source, and FIG. 3 (b) is an electrode configuration diagram of the plasma ion source, in which the movement of the ion beam is schematically shown.
In the present invention, at a position separated from the ionization chamber 1a to the downstream side by the same distance as the width of the slit 15 of the acceleration electrode 1b,
The extraction electrode 1g is provided as an auxiliary electrode, and the applied voltage to the extraction electrode 1g is determined based on the state of the ion source.

The ions generated in the ion generation region 2a at the center of the ionization chamber 1a are repelled by the repeller electrode 1f to which a positive voltage is applied by several volts than the acceleration electrode 1b, and are pushed out toward the acceleration electrode 1b. . However, the initial velocity of the generated ions is disturbed due to thermal motion and collision of electrons, and the electric field generated by the repeller electrode 1f cannot efficiently pass through the slit 15 of the acceleration electrode 1b.

Therefore, in the present invention, the width of the slit 15 of the acceleration electrode 1b is made wider than the width of the slit 16 of the extraction electrode 1g, and the distance between the extraction electrode 1g provided on the downstream side of the acceleration electrode 1b and the acceleration electrode 1b. Is set to be approximately equal to the distance between the acceleration electrode 1b and the ion generation region 2a.

Therefore, the electric field leaked from the slit 15 of the acceleration electrode 1b into the ionization chamber 1a is generated in the ion generation region 2a.
It spreads to the vicinity, the position of the crossover point of the ion beam 2 is on the downstream side of the extraction electrode 1g, and the ion beam 2 is efficiently extracted from the slit 15 by the leakage electric field (permeation electric field) and transmitted through the slit 16 of the extraction electrode 1g. Can be made. Since such an osmotic electric field is rapidly attenuated as the distance from the slit is increased, the ion generation region 2a
The increase of the electric field inside is slight, and the increase of the energy dispersion of the ion beam 2 is not a problem.

On the other hand, in the case of the plasma ion source of FIG. 3 (b), a sheath region having a length several times the Debye length is formed between the acceleration electrode 1b and the plasma 2b. Plasma 2b
Has a potential higher than the accelerating electrode 1b by several volts to several tens of volts, and efficiently accelerates the ion beam 2 toward the accelerating electrode 1b. The voltage at this time is called plasma floating potential, which is about 6 times the electron temperature, which is one of the most important parameters of plasma.

Since the ions are emitted from the entire surface of the plasma, an ion current amount that is approximately proportional to the width of the slit 15 of the acceleration electrode 1b can be obtained. However, since the spherical aberration is larger at the ends of the slit 15 than in the vicinity of the center, the slit 1
Ions that have passed through the end of 5 are excessively focused and increase the angular dispersion. Therefore, in order to cancel this excessive convergence, the width of the slit 16 of the extraction electrode 1g is narrowed similarly to the width of the ion beam 2. That is, by setting the cut angle of the slit 16 to be π−θ with respect to the cut angle θ of the slit 15, the spherical aberration of the slit 15 is canceled by the spherical aberration of the slit 16, and the overall spherical aberration is reduced, resulting in an angular dispersion. It is possible to obtain an ion beam 2 having a small size.

FIG. 4 is a diagram showing the relationship between the ratio f / d of the focal length f to the electrode spacing d of the two electrodes and the ratio Φ2 / Φ1 of the outgoing energy Φ2 to the incident energy Φ1. When this is applied to the case of FIG. 3A, Φ1 is ½ of the potential difference between the repeller electrode 1f and the acceleration electrode 1b.
2-Φ1 corresponds to the potential difference between the acceleration electrode 1b and the extraction electrode 1g. When the focal length f is short, the angular dispersion of the beam increases, which is not preferable. In order to reduce the angular dispersion, it is necessary to lengthen the focal length f and form a crossover at which the beam converges at its narrowest on the downstream side of the extraction electrode 1g. Quantitatively, it is understood that the voltage applied to the extraction electrode 1g may be set so as to satisfy Φ2 / Φ1 <5.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is an overall configuration diagram of a mass spectrometer according to an embodiment of the present invention, FIG. 1 is a configuration diagram of an ion source according to the present invention, (a) is a diagram showing a longitudinal section, and (b) is a diagram. [Fig. 3] is a view of (a) taken along the line AA. The mass spectrometer of this embodiment is of a double focusing type. Ions generated by the ion source 1 are extracted and become a high-quality ion beam 2 having excellent focusing properties,
The ion beam 2 is diffused by the quadrupole lens 7a and then mass-separated by the sector magnetic field 3. After the ion beam 2 is mass-separated, it is converged by the quadrupole lens 7b and the sector electric field 4
The energy is discriminated by and finally the mass separation slit 5
The ion current that has passed through is measured by the detector 6. The measurement result is stored in the operation control / measurement data processing unit 10 as a mass spectrum.

In this embodiment, in order to automatically set the approximate voltage conditions of the ion beam extraction electrode system, for example, in the case of an electron impact ionization ion source, the repeller electrode voltage 12d is input to the ion source state monitoring unit 11, Extraction electrode voltage 12g
The predicted value 12e of 12 is output to the extraction power source 9. In the case of the plasma ion source, it is difficult to directly measure the plasma floating potential, but in the sector electric field, the sum Vacc of the acceleration electrode voltage Vacc and the plasma floating potential Vp, which is the actual acceleration voltage.
The plasma floating potential Vp can be estimated by paying attention to the fact that the relationship of the orbit radius R with respect to + Vp can be expressed by Equation 1.

[0020]

## EQU1 ## R = 2 (Vacc + Vp) / E (Equation 1) where E is the strength of the electric field of the sector electric field.

Although the voltage of the extraction electrode 1g thus obtained is a good predicted value, it is not always the optimum value. Therefore, the ion source state monitoring unit 11 inputs the current signal 12a of the ion current monitor 8a provided on the beam line and adjusts the voltage of the extraction electrode system so that the current value becomes maximum.

The detailed structure of the ion source and the simplest method for setting the extraction electrode voltage will be described with reference to FIG. The entire ion source is equipped with an electrode support insulator 1 in a vacuum container 18 on the beam line of the analysis unit.
7 and the inside of the ion source is kept in vacuum by the vacuum container 14. A-A in FIG.
As shown in the cross section, the extraction electrode 1g is composed of upper and lower plate-shaped electrodes, and the acceleration electrode 1b is a plate-shaped electrode having a rectangular opening. The ion source state monitoring unit 11 sets the voltage 12g of the extraction electrode 1g based on the voltage 12d of the repeller electrode 1f. Next, the amount of current passing through the slits 15 and 16 is measured by the ion current monitor 8a, and the voltage 12f of the focusing electrode 1c is adjusted so that this current becomes maximum. In the example of FIG. 1, the extraction power supply 9 is shared as the power supply for the focusing electrode 1c and the power supply for the extraction electrode 1g. In this case, electrodes 1c and 1
The applied voltage of g may be the same voltage. By doing so, it is possible to save the power supply, but it goes without saying that separate power supplies may be prepared.

5 and 6 are diagrams showing the results of confirming the effects of this embodiment by numerical simulation. FIG. 5 is a simulation result of an electron impact ionization ion source, and FIG. 5A is a simulation result of a conventional ion source. Here, the acceleration electrode voltage Vacc is 6.000k.
V, the repeller electrode voltage Vr is 6.003 kV, and the accelerating electrode slit width is 0.5 mm. Ions have an isotropic initial velocity equivalent to 0.01 eV, and the beam width expands as they approach the accelerating electrode, so there is a component that cannot pass through the slit of the accelerating electrode. Moreover, since the ion beam is rapidly converged in the slit, it has a large angular dispersion. The beam width spreads over 1 mm near the focusing electrode,
It makes it difficult to converge the beam thereafter. In such a situation, it is not effective to increase the slit width of the acceleration electrode to increase the current amount of the ion beam,
It just increases the dead current.

On the other hand, in this embodiment of FIG. 5B, the slit width of the acceleration electrode is 1 mm and the slit width of the extraction electrode is 0.5 m.
m, and Vex = 5990V is applied to the extraction electrode. The electric field seeps out from the wide slit of the accelerating electrode to the vicinity of the ion generation region and succeeds in extracting all isotropically emitted ions. The focal length at the extraction electrode 1g changes greatly only by adjusting Vex by several volts, and it is easy to control the angular dispersion of the beam. For these reasons, it was confirmed that in this embodiment, the amount of current is about twice and the angular dispersion is about 1/2 as compared with the conventional one. Further, since the width of the slit 16 of the extraction electrode 1g is narrow, the ionization chamber 1a
There is an additional effect that the internal gas pressure is high and the vacuum degree on the beam line is low.

FIG. 6 shows simulation results of the plasma ion source. (A) shows a case where the plasma floating potential Vp is 30V, (b) shows a case where Vp is 60V, and (c) shows a case where Vp is 60V.
Each case where the voltage condition is optimally controlled by V is shown. In FIG. 6, the reference acceleration electrode voltage Vacc is fixed at 6.00 kV, and the floating potential of plasma with respect to Vacc is represented by Vp. The optimum extraction electrode voltage Vex in (a) of Vp = 30V was 5.88 kV. In this case, Vacc
The potential difference between Vex and Vex is 120V. Next, FIG. 6 (b)
Therefore, if Vp is raised to 60V while Vex is fixed, the ion beam will not converge. Therefore, in response to the double increase of Vp from 30V to 60V, Vp
By doubling the potential difference between acc and Vex from 120V to 240V, that is, by adjusting Vex to 5.760kV, an almost optimally focused ion beam is obtained as shown in FIG. 6 (c). be able to.

[0026]

As described above, according to the present invention,
By measuring the state of the ion source, a high-current ion beam with a small angle dispersion can be easily obtained, and the mass spectrometer can be made highly sensitive.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an ion source according to an embodiment of the present invention,
(a) is a figure which shows a vertical cross section, (b) is an AA arrow view of (a).

FIG. 2 is an overall configuration diagram of a mass spectrometer according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining the principle of angular dispersion reduction by the ion source of the present invention, in which (a) is an electron impact ionization ion source,
(B) shows the case of a plasma ion source.

FIG. 4 is a diagram showing a relationship between an extraction electrode voltage and a focal length.

FIG. 5 is a diagram showing a numerical simulation result of an electron impact ionization ion source, in which (a) is a conventional ion source;
(B) is a diagram showing a case of the ion source of the present embodiment.

FIG. 6 is a diagram showing a numerical simulation result of a plasma ion source. (A) shows a case where the plasma floating potential Vp is 30V, (b) shows a case where Vp is 60V, and (c) shows a case where Vp is 6V.
It is a figure which shows the case where the voltage condition is optimally controlled by 0V.

FIG. 7 is a cross-sectional view of a conventional ion source and beam extraction electrode system.

[Explanation of symbols]

1 ... Ion source, 1a ... Ionization chamber, 1b ... Accelerating electrode, 1
c ... focusing electrode, 1d ... ground electrode, 1e ... exit slit,
1f ... Repeller electrode, 1g ... Extraction electrode, 2 ... Ion beam, 2a ... Ion generation region, 2b ... Plasma, 2c ... Crossover, 3 ... Sector magnetic field, 4 ... Sector electric field, 5 ...
Mass separation slit, 6 ... Detector, 7a, 7b ... Quadrupole lens, 8a ... Ion current monitor, 9 ... Extraction power supply, 10 ...
Operation control / measurement data processing unit, 11 ... Ion source state monitoring unit, 13 ... Analysis unit power supply.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Mimura 882 Ichige, Ichima, Hitachinaka City, Ibaraki Prefecture Hitachi, Ltd. Measuring Instruments Division

Claims (13)

[Claims] 1. An ion source in which ions generated in an ion generation region are extracted from a slit of an accelerating electrode to form an ion beam, and the ion beam is converged by a converging electrode and emitted from an emission slit. An ion source, wherein an extraction electrode for separating a crossover point of the generated ion beam from the acceleration electrode by a required distance is provided in the vicinity of the downstream of the acceleration electrode. 2. An ion source in which ions generated in an ion generation region are extracted from a slit of an accelerating electrode to form an ion beam, and the ion beam is converged by a converging electrode and emitted from an emission slit. 2. An ion source, wherein an extraction electrode having a small slit is provided at a position separated to the downstream side of the acceleration electrode by the same extent as the distance between the acceleration electrode and the ion generation region. 3. The ion source according to claim 1 or 2, wherein the spherical aberration received by the ion beam by the slit of the acceleration electrode is offset by the influence of the slit of the extraction electrode. 4. The cutting angle of the slit of the acceleration electrode is π with respect to the cutting angle θ of the slit of the acceleration electrode.
An ion source having a configuration of canceling spherical aberration by setting −θ. 5. A mass spectrometer for measuring an ion current amount of a specific mass by extracting ions generated by an ion source by an extraction electrode system to generate an ion beam and separating the ions into orbits specific to the mass of the ion in an electromagnetic field. A mass spectrometer, wherein the ion source according to any one of claims 1 to 4 is used as an ion source. 6. An ion source, a first quadrupole lens for diffusing the ion beam extracted from the ion source, and a sector magnetic field device for mass-separating the ion beam diffused by the first quadrupole lens, A second quadrupole lens for converging the ion beam mass-separated by the sector magnetic field device, a sector electric field for discriminating the energy of the ion beam converged by the second quadrupole lens, and a post-stage of the sector electric field device 5. A double-focusing mass spectrometer, comprising: a mass separation slit placed on a substrate; and a detector for measuring an ion current transmitted through the mass separation slit, wherein the ion source is any one of claims 1 to 4. A mass spectrometer using the ion source according to 1. 7. The mass spectrometer according to claim 5, wherein the voltage condition applied to the extraction electrode is set from the voltage condition of the ion source. 8. The ion source according to claim 7, wherein the ion source is an electron impact ionization ion source, and based on the voltage of the repeller electrode that pushes out the ions generated by the ion source to the extraction electrode side,
A mass spectrometer characterized by setting a voltage condition applied to an extraction electrode. 9. The method according to claim 7, wherein the voltage condition of the extraction electrode is adjusted based on the measured value of the ion current monitor installed on the ion beam line, and the voltage condition is adjusted to maximize the ion current amount. Mass spectrometer. 10. The mass spectrometer according to claim 7, wherein the ion source is a plasma ion source and a voltage condition to be applied to the extraction electrode is set based on a plasma floating potential. 11. The mass spectrometer according to claim 10, wherein the plasma floating potential is obtained by using a radius of gyration of ions in an electromagnetic field. 12. A mass spectrometer for detecting ions having a specific mass by extracting ions generated by an ion source by an extraction electrode system to generate an ion beam and allowing the ion beam to pass through an electromagnetic field. The system is provided with an accelerating electrode having a slit for extracting ions from the ion source, and is provided in the vicinity of the downstream of the accelerating electrode, and requires a crossover point of the ion beam extracted from the accelerating electrode slit from the accelerating electrode. A mass spectrometer, comprising: an extraction electrode for separating by a distance. 13. A mass spectrometer for detecting ions having a specific mass by extracting ions generated in an ion generation region by an extraction electrode system to generate an ion beam and allowing the ion beam to pass through an electromagnetic field. The electrode system includes an acceleration electrode having a slit for extracting ions from the ion generation region, and an extraction electrode having a slit having a width smaller than the slit of the acceleration electrode, and between the acceleration electrode and the ion generation region. The mass spectrometer, wherein the extraction electrode is provided at a position that is separated from the acceleration electrode by a distance substantially equal to the distance.